Foamed isocyanate-based polymers are known in the art and one advantage of isocyanate-based polymers compared to other polymer systems is that polymerization and foaming can occur in situ. This results in the ability to mould the polymer while it is forming and expanding. There is however a growing need for development of novel load building techniques for the foams. In order to confer the load building properties normally relatively expensive materials are used and thereto also other properties of the foams could be improved compared to conventionally used techniques.
One of the conventional ways to produce polyurethane foam is known as the “one-shot” technique. In this technique, the isocyanate, a suitable polyol, a catalyst, water (which acts as a reactive “blowing” agent and can optionally be supplemented with one or more physical blowing agents) and other additives are mixed together using, for example, impingement mixing (e.g., high pressure). Generally, if a polyurea is produced, the polyol is replaced with a suitable polyamine. A polyisocyanurate may result from cyclotrimerization of the isocyanate component. Urethane modified polyureas or polyisocyanurates are known in the art. In either scenario, the reactants would be intimately mixed very quickly using a suitable mixing technique.
Another technique for producing foamed isocyanate-based polymers is known as the “prepolymer” technique. In this technique, a prepolymer is produced by reacting polyol and isocyanate (in the case of a polyurethane) in an inert atmosphere to form a liquid polymer terminated with reactive groups (e.g., isocyanate moieties and active hydrogen moieties). Typically the prepolymer is produced with an excess of isocyanate groups so all the active hydrogen groups are reacted. To produce the foamed polymer, the prepolymer is thoroughly mixed with a lower molecular weight polyol (in the case of producing a polyurethane) or a polyamine (in the case of producing a modified polyurea) in the presence of a curing agent and other additives, as needed.
Regardless of the technique used, it is known in the art to include a filler material in the reaction mixture. Conventionally, filler materials have been introduced into foamed polymers by loading the filler material into one or both of the liquid isocyanate and the liquid active hydrogen-containing compound (i.e., the polyol in the case of polyurethane, the polyamine in the case of polyurea, etc.). Generally, incorporation of the filler material serves the purpose of conferring so-called load building properties to the resulting foam product.
The nature and relative amounts of filler materials used in the reaction mixture can vary, to a certain extent, depending on the desired physical properties of the foamed polymer product, and limitations imposed by mixing techniques, the stability of the system and equipment imposed limitations (e.g., due to the particle size of the filler material being incompatible with narrow passages, orifices and the like of the equipment).
One known technique of incorporating a solid material in the foam product for the purpose of improving hardness properties involves the use of polyol-solids dispersion, particularly one in the form of a polymer polyol, i.e. a graft copolymer polyol. As is known in the art, graft copolymer polyols (copolymer polyols) are polyols, preferably polyether polyols, which contain other organic polymers. It is known that such graft copolymer polyols are useful to confer hardness (i.e., load building) to the resultant polyurethane foam compared to the use of polyols which have not been modified by incorporating the organic polymers. Within graft copolymer polyols, there are two main categories which may be discussed: (i) chain-growth copolymer polyols, and (ii) step-growth copolymer polyols.
Chain-growth copolymer polyols generally are prepared by free radical polymerization of monomers in a polyol carrier to produce a free radical polymer dispersed in the polyol carrier. Conventionally, the free radical polymer can be based on acrylonitrile or styrene-acrylonitrile (SAN). The solids content of the polyol is typically up to about 60%, usually in the range of from about 15% to about 40%, by weight of the total weight of the composition (i.e., free radical polymer and polyol carrier). Generally, these chain-growth copolymer polyols have a viscosity in the range of from about 1,000 to about 8,000 centipoise. When producing such chain-growth copolymer polyols, it is known to induce grafting of the polyol chains to the free-radical polymer.
Step-growth copolymer polyols generally are characterized as follows: (i) PHD (Polyhamstoff Disperion) polyols, (ii) PIPA (Poly Isocyanate Poly Addition) polyols, and (iii) epoxy dispersion polyols. PHD polyols are dispersions of polyurea particles in conventional polyols and generally are formed by the reaction of a diamine (e.g., hydrazine) with a diisocyanate (e.g., toluene diisocyanate) in the presence of a polyether polyol. The solids content of the PHD polyols is typically up to about 50%, usually in the range of from about 15% to about 40%, by weight of the total weight of the composition (i.e., polyurea particles and polyol carrier). Generally, PHD polyols have a viscosity in the range of from about 2,000 to about 6,000 centipoises. PIPA polyols are similar to PHD polyols but contain polyurethane particles instead of polyurea particles. The polyurethane particles in PIPA polyols are formed in situ by reaction of an isocyanate and alkanolamine (e.g., triethanolamine). The solids content of the PIPA polyols is typically up to about 80%, usually in the range of from about 15% to about 70%, by weight of the total weight of the composition (i.e., polyurethane particles and polyol carrier). Generally, PIPA polyols have a viscosity in the range of from about 4,000 to about 50,000 centipoises. See, for example, U.S. Pat. Nos. 4,374,209 and 5,292,778. Epoxy dispersion polyols are based on dispersions of cured epoxy resins in conventional based polyols. The epoxy particles are purportedly high modulus solids with improved hydrogen bonding characteristics.
Further information regarding useful graft copolymer polyols may be found, for example, in Chapter 2 of “Flexible Polyurethane Foams” by Herrington and Hock (1997) and the references cited therein.
Untreated carbohydrates have been incorporated as direct additives into isocyanate-based polymer foams in two ways—1) as a partial or complete replacement for the polyol component, and 2) as an unreacted additive or filler. The carbohydrate can be introduced into the foam starting materials either as a solution or as a fine solid. When added as a solution, the hydroxyl groups on the carbohydrate can react with the isocyanate component and become chemically incorporated into the structure of the polyurethane. Examples of carbohydrates include certain starches, corn syrup, cellulose, pectin as described in U.S. Pat. No. 4,520,139, mono- and disaccharides as described in U.S. Pat. Nos. RE31,757, 4,400,475, 4,404,294, 4,417,998, oligosaccharides as described in U.S. Pat. No. 4,404,295 and pregelatinized starch as described in U.S. Pat. No. 4,197,372. As a solid dispersion, the carbohydrate may be inert in the polymerization reaction, but is physically incorporated into the foam. The advantage is lower cost and the ability of the carbohydrates to char upon combustion, preventing further burning and/or dripping of the foam and reducing smoke formation as described in U.S. Pat. Nos. 3,956,202, 4,237,182, 4,458,034, 4,520,139, 4,654,375. Starch and cellulose are commonly used for this purpose. The starch or cellulose may also be chemically modified prior to foam formulation as described in U.S. Pat. Nos. 3,956,202 and 4,458,034 and US application 2004/0014829 where compositions of polyether polyols derived from alkoxylated hydrogenated starch hydrolysates (HSH) are used.
Further the use of dendritic macromolecules in isocyanate based foams is described in U.S. Pat. No. 5,418,301, WO 02/10189 and US applications US 2003/0236315 and US 2003/0236316 and the use of highly branched polysaccharides with a higher functionality in isocyanate based foams is described in US applications US 2006/0122286 and US 2006/0241199.
Despite the advances made in the art, there exists a continued need for the development of novel load building techniques. Specifically, many of the prior art approaches discussed hereinabove involve the use of relatively expensive materials (e.g., the graft copolymer polyols described above) which can be complicated to utilize in a commercial size facility. Thus, it would be desirable to have a load building technique which could be conveniently applied to isocyanate-based foams as an alternative to conventional load building techniques. It would be further desirable if the load building technique was relatively inexpensive, load building compounds used had good compability with other parts of the reaction mixture and/or improved other properties of the foam and/or could be incorporated into an existing production scheme without great difficulty.
It should be noted that all documents cited in this text (“herein cited documents”) as well as each document or reference cited in each of the herein-cited documents, and all manufacturer's literature, specifications, instructions, product data sheets, material data sheets, and the like, as to the products and processes mentioned in this text, are hereby expressly incorporated herein by reference.